The data flow of different sources (e.g., several users, several services or several terminals) must be combined and connected in an efficient way in order to perform access and aggregation tasks. Currently, broadband access nodes connected to an Ethernet aggregation network typically support two main logical connectivity models (i.e., conventional connectivity models). These two conventional connectivity models are aggregation model and transparent cross connection model.
In aggregation mode, a broadband access node combines the traffic from multiple subscribers or logical channels on a subscriber's loop onto 1 or more logical identifiers in an aggregation network. Typically, a per-service logical identifier, for instance a Virtual Local Area Network (VLAN), is used on the Ethernet aggregation network. Consolidating traffic can be achieved at Layer 2 (i.e., the Data Link Layer) through a bridging function or at Layer 3 (i.e., the Network Layer) through Internet Protocol (IP) forwarding function. This aggregation mode allows for a very efficient multicast infrastructure and the implementation of per-subscriber security and traffic policing at the aggregation or services edge of the network.
However, combining traffic from multiple subscribers through such an aggregation mode at the access node requires that certain function be enabled at the access node. Examples these functions include, but are not limited to, enforcement of per-subscriber security policies, enforcement of per-subscriber traffic/Quality of Service (QoS) policies, generation of billing records and lawful intercept of information. The aggregation mode of operation forces these functions to be further distributed into the broadband access node. Traditionally, a Broadband Remote Access Aggregation Server (BRAS) or Edge Router in a network has performed these functions by adding a session-based protocol to identify a subscriber and enforce policies
In transparent cross connect mode, a broadband access node does not consolidate traffic from multiple subscribers or logical channels on a subscriber's loop. The broadband access node performs a direct transparent forwarding of the data from the subscriber's logical channel to a VLAN identifier on the Ethernet aggregation link. The combination of traffic of different subscribers in this mode is performed by more centrally-located network nodes. Accordingly, this model allows for per-subscriber security and traffic policies to be enforced by a centralized network node but not by the access node itself.
When operating in transparent cross connection mode, the broadband access node performs a transparent mapping of a local loop logical circuit to a unique VLAN identifier on the aggregation link. Because of this transparent mapping, no traffic in the access node is consolidated and, thus, allowing for this consolidation functionality to remain in the BRAS or Edge Router. Furthermore, when cross connectivity is facilitated in a transparent manner, the broadband access node cannot become a replication point for multicast traffic, cannot filter packets, cannot change the order of packets, cannot insert packets in the data stream and cannot enforce per-subscriber policies or security policies (e.g., enforcement of per-subscriber security policies, enforcement of per-subscriber traffic/QoS policies, generation of billing records and lawful intercept of information).
Therefore, implementation of cross connection functionality in an access node in a manner that overcomes limitations associated with conventional approaches for implementing cross connection functionality in an access node is useful and advantageous.